1. Field of the Invention
The present invention relates to a method and apparatus for lapping a magnetic head slider or a thin-film magnetic head so as to adjust an element height of the thin-film magnetic head, and to a manufacturing method of a thin-film magnetic head.
2. Description of the Related Art
Recently, in order to satisfy demand for higher recording capacity in a hard disk drive (HDD) apparatus, required are downsizing, narrowing of track and narrowing of gap in a thin-film magnetic head. Thus, when adjusting an element height of the magnetic head slider or the thin-film magnetic head, it is necessary to perform a precise and productive polishing process.
According to the conventional manufacturing method of a thin-film magnetic head, typically, a wafer provided with many magnetic head elements is first cut to separate into a plurality of row bars each of which has a plurality of the magnetic head elements aligned. Then, each row bar is lapped so as to adjust its element height to a defined size. When performing this lapping process, the row bar is pressed to a rotating lapping plate at a predetermined pressure to lap an air bearing surface (ABS) of the row bar.
In order to correctly adjust an element height such as for example a height of a magnetoresistive effect (MR) read head element (MR height, MRH) to a desired value, each row bar has a plurality of lapping control sensors formed by an MR film, called as resistance lapping guide (RLG) sensors, and electrical signals from these RLG sensors are monitored to control an amount of lapping.
However, when the MR read head element becomes extremely reduced in size, it becomes difficult to precisely recognize relationship in location between the MR read head elements and the RLG sensors in the row bar within its machining accuracy. As a result, resistance values of the MR read head elements in the row bar may greatly fluctuate.
If actual MR read head elements are used instead of the dedicated RLG sensors as the lapping control sensors and a lapping amount is obtained by monitoring resistance values of these actual MR read head elements, the aforementioned problem may be resolved. However, it should be noted that each actual MR read head element has lower and upper shield layers, and that a gap between the lower and upper shield layer and also a gap between each shield layer and the MR multi-layered structure are very narrow because of the micro size of the MR read head element. Therefore, smears or phenomenon in which the upper shield layer or the lower shield layer partially extends in the lapping direction due to its ductile property may sporadically occur during lapping. If smears occur, because the smears result electrical short circuits to reduce element resistance values to approximately zero, it becomes impossible to monitor correct element resistance values.